lvfontbin behaves different as .mpy and .py

[FoamyGuy]

Adafruit CircuitPython 10.0.0-alpha.7-5-g203c9990e6-dirty on 2025-06-25; Adafruit Fruit Jam with rp2350b

With this code:

import gc

from displayio import Group, TileGrid, Palette
from terminalio import Terminal, FONT

from adafruit_bitmap_font import bitmap_font
import supervisor

main_group = Group()
display = supervisor.runtime.display
display.root_group = main_group

print(f"free: {gc.mem_free()}")
# font = FONT
font = bitmap_font.load_font("fonts/terminal.lvfontbin")
char_size = font.get_bounding_box()
print(f"char_size: {char_size}")
screen_size = (display.width // char_size[0], display.height // char_size[1])

terminal_palette = Palette(2)
terminal_palette[0] = 0x000000
terminal_palette[1] = 0xffffff

terminal_area = TileGrid(bitmap=font.bitmap, width=screen_size[0], height=screen_size[1],
                         tile_width=char_size[0], tile_height=char_size[1], pixel_shader=terminal_palette)

main_group.append(terminal_area)
terminal = Terminal(terminal_area, font)

message = f"Hello World"
terminal.write(message)

while True:
    pass

when adafruit_bitmap_font is mpy files:

code.py output:
free: 8262784
Traceback (most recent call last):
  File "code.py", line 15, in <module>
  File "adafruit_bitmap_font/bitmap_font.py", line 71, in load_font
  File "adafruit_bitmap_font/lvfontbin.py", line 77, in __init__
MemoryError: memory allocation failed, allocating 28161 bytes

and when adafruit_bitmap_font is py files instead:

code.py output:
free: 8262768
char_size: (0, 16, 0, -4)
Traceback (most recent call last):
  File "code.py", line 18, in <module>
ZeroDivisionError: division by zero

The divide by zero error I think is unrelated to the difference in behavior between mpy and py, it seems to be due to lvfont having different values for bounding box than the code I am using had expected.

This issue is specifically for the fact that load_font() raises memory error when run as .mpy files but suceeds when run as .py files.

[FoamyGuy]

There is more than meets the eye here. I've realized that the Fruit Jam OS launcher uses lvfontbin and manages to load font files just fine on the same hardware even when the library is mpy.

[FoamyGuy]

It seems that when load_font() it matters how much memory is free at that moment. If I add l = [1024] * 1024 after the imports to arbitrarily use up some more space before attempting to load the font then the font load succeeds.